1. Field of the Invention
The present invention relates to an image display unit which displays a picture data with an aspect ratio of 16:9 by a letter box display, a system, and a method.
As a picture signal (picture data) contained in a High Definition Television (HDTV) and a Digital Versatile Disc (DVD) or the like, there is a picture data in which the ratio of width to height (aspect ratio) of the picture is 16:9. When an image with an aspect ratio of 16:9 is displayed on a display with an aspect ratio of 4:3 as it is, the image is vertically distorted.
2. Description of the Prior Art
As a conventional system of displaying a picture data (signal) with an aspect ratio of 16:9 on a display with an aspect ratio of 4:3, there are a pan scanning system and a letter box system. In the pan scanning system, both ends of a picture are cut off and the picture at the center is displayed with an aspect ratio of 4:3. In the letter box system, black frames are displayed at the upper and lower parts of a display frame, and between the upper and lower black frames, a picture data (signal) with an aspect ratio of 16:9 is displayed by being contracted.
Referring to FIG. 8, a display method according to a conventional letter box system will be described.
In a conventional letter box display, black frames are coated (black data is transferred) at the upper and lower parts of a screen 202 with an aspect ratio of 4:3, and between the upper and lower black frames, a picture data (signal) with an aspect ratio of 16:9 which is vertically contracted (contraction by ¾) is displayed. Thus, in the conventional letter box system, from a picture data (signal) with an aspect ratio of 16:9, the data in the vertical direction is contracted by ¾ in size, and the display has been performed on a display unit together with the upper and lower black frames.
However, this method creates a problem. The reason is that when a central processing unit (CPU) performing the multiprocessing performs all processing, it takes a long time for the contraction processing.
Furthermore, this conventional letter box system produces a problem. The reason is that the contraction processing is performed for each frame, so that the throughput of the data may be increased and the load of the central processing unit (CPU) may be raised. Accordingly, when the speed of the processing such as a decoding processing by a software of an MPEG picture data is taken seriously, a high performance of the central processing unit (CPU) is required.
Furthermore, a problem is caused. The reason is that the scanning conversion processing becomes complex. In the case where an image of a picture data of the interlace scanning system (interlaced scanning) is displayed on a display unit of the sequential scanning such as a display unit of a PC, the scanning conversion processing is required. The vertical contraction by ¾ creates a difference in the number (of scanning lines) between a first (odd number) field and a second (even number) field.